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Re: [Discuss-gnuradio] How to modify freq deviation in a FM radio?????

From: nansai hu
Subject: Re: [Discuss-gnuradio] How to modify freq deviation in a FM radio?????
Date: Wed, 28 Oct 2009 12:19:38 -0400

Yes,this seems work.but the intention is get a radio.So, I use a USRP source instead FFT sink and observe in Spectrum Analyzer and it still doesn't work.
I think the only different is I use a usrp as CF to put baseband FM signal to RF because Spectrum Analyzer quite like FFT sink.

2009/10/28 Josh Blum <address@hidden>
My advice is to get this all figured out in software before using any hardware (usrps and spectrum analyzers).

You can simulate the effect of changing the max deviation all in software using a noise source, throttle, nbfm tx block, and an fft sink (all in grc).

I guarantee that changing max deviation from 5 to 50k makes a big difference.


nansai hu wrote:
I want to design a FM radio with freq deviation can be change.
Then I tried to modified an example in GNUradio example folder which name
"fm_tx4.py" in line61,let max_dev=5 to 50K,shown in following yellow label.
but there is no change at all in a spectrum analyzer.
Help me,thanks

class pipeline(gr.hier_block2):
   def __init__(self, filename, lo_freq, audio_rate, if_rate):

       gr.hier_block2.__init__(self, "pipeline",
                               gr.io_signature(0, 0, 0),
# Input signature
                               gr.io_signature(1, 1, gr.sizeof_gr_complex))
# Output signature

       src = "" (gr.sizeof_float,'/home/sdr/Desktop/hu/1.wma',
       fmtx = blks2.nbfm_tx (audio_rate, if_rate, max_dev=5, tau=75e-6)

       # Local oscillator
       lo = gr.sig_source_c (if_rate,        # sample rate
                             gr.GR_SIN_WAVE, # waveform type
                             lo_freq,        #frequency
                             1.0,            # amplitude
                             0)              # DC Offset
       mixer = gr.multiply_cc ()

       self.connect (src, fmtx, (mixer, 0))
       self.connect (lo, (mixer, 1))
       self.connect (mixer, self)


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